1. Field of the Invention
The present invention relates to a valve timing control apparatus for controlling a valve timing of a valve, which is opened and closed by a camshaft according to a torque transmitted from a crankshaft in an internal combustion engine, by utilizing a working fluid supplied from a supply source.
2. Description of Related Art
Conventionally, a known valve timing control apparatus includes a housing, which is rotatable with rotation of a crankshaft, and a vane rotor, which is rotatable with rotation of a camshaft. JP-A-2010-285918 (US 2010/0313835 A1) describes a valve timing control apparatus in which a rotation phase of a vane rotor is changed toward advance side or retard side relative to a housing by introducing working fluid into an advance chamber or a retard chamber which are separated from each other in a rotation direction by the vane rotor in the housing.
The rotation phase is locked by a lock portion when the working fluid is discharged from a lock chamber, and is unlocked by the lock portion when the working fluid is introduced into the lock chamber. The working fluid discharged from or introduced into the lock chamber is controlled at the same timing as the working fluid discharged from or introduced into the advance/retard chamber by a control valve through a reciprocation of a spool in an axis direction.
The spool is moved based on a balance between a driving force of an electromagnetic solenoid and a biasing force of a spring. A moving area of the spool is set to have a variable region and a lock region. When the driving force is defined to be applied in a first direction, the biasing force is applied in a second direction opposite from the first direction, in the axis direction.
In the variable region, a lock activation port communicating with the lock chamber and an introduction port through which the working fluid is introduced into the advance chamber are connected to a supply port to which the working fluid is supplied from the supply source. In this case, the rotation phase, that is not locked, is changed into the advance side.
In the lock region, the introduction port is connected to the supply port, and the lock activation port is connected to a drain port from which the working fluid is discharged. In this case, the rotation phase is locked in a state that the advance chamber is filled with the working fluid. When the spool is moved from the lock region to the variable region, the working fluid can be introduced into the advance chamber that is already filled with the working fluid, so that the rotation phase can be quickly changed into the advance side.
Further, a part of the lock region is set as a throttle region at which a flowing amount of the working fluid is reduced from the supply port to the introduction port. In a case where the spool is moved from the variable region to the throttle region, the amount of the working fluid introduced into the advance chamber from the introduction port is reduced, so that advance-side variation amount of the rotation phase can be reduced. Thus, the vane rotor can be easily locked into a predetermined phase.
However, when the driving force is not applied to the spool, the spool reaches an end position of a movable area in the second direction. At a fail time when the driving force is not applied to the spool, the spool reaches the movable end position in the second direction. At this time, the flowing amount of the working fluid from the supply port to the introduction port is increased compared with the case of the throttle region, because the throttle region is located to be depart from the end position of the spool in the first direction. That is, at the fail time, the amount of the working fluid introduced into the advance chamber and the advance-side variation amount of the rotation phase are increased, so that it becomes difficult for the vane rotor to be locked into the predetermined phase. If the rotation phase cannot be locked at the fail time, the engine may have failure such as knocking, stall, or activation error.